A related art ink jet head attached to an ink jet printer has been known as one of the liquid discharge heads for discharging a liquid. Some ink jet heads are provided with a passage unit in which a common ink chamber and a plurality of individual ink passages from the common ink chamber to nozzles are formed, and a reservoir unit in which a reservoir communicating with the common ink chamber and an ink supply port for supplying ink to the reservoir are formed. In such a related art ink jet head, ink is supplied into a reservoir of the reservoir unit via an ink tube that functions as an ink supply passage connected to an ink supply port. However, sometimes air remaining in an ink tube is introduced into the reservoir along with ink via an ink supply port by a pump which sends ink into the reservoir. Air in the reservoir causes clogging of minute nozzles. If a nozzle is clogged, the discharge performance of ink drops is worsened. Therefore, JP-A-2007-268868 describes a related art ink jet head in which an ink ejection port for discharging air in the reservoir to the outside is formed, and at the same time, an ink tube functioning as an ink ejection passage is connected to the ink ejection port.
Also, JP-A-2007-268829 describes a related art reservoir unit having a plate-shaped passage component. An annular projection protruding in a direction orthogonal to one surface of the passage component is formed on the corresponding surface. A film is adhered to the tip end of the annular projection, and a spacing surrounded by the inner circumferential surface of the annular projection and the film forms a part of the ink passage. Therefore, a radical fluctuation in pressure of ink in the reservoir unit can be absorbed by flexing of the film. This flexing acts as a damper function. In addition, surrounding the annular projection in the passage component, a rib protruding in the direction orthogonal to the surface is formed in order to prevent deformation by increasing the rigidity of the passage component.
Where two passages of an ink supply passage and an ink ejection passage, which are connected to an ink supply port and an ink ejection port of the ink jet head described in JP-A-2007-268868 described above, respectively, are formed on an attachment detachable from the ink jet head, it becomes possible to connect the two passages to the ink jet head by a single operation. However, the attachment having two passages thus mounted therein is liable to be large-sized.
Also, where there is unevenness between the pitch of the ink supply port and the ink ejection port, which are formed in the ink jet head, and the pitch of connection portions of the ink supply port and the ink ejection port, which are formed in the attachment, a connection between both cannot be normally carried out. That is, in such a case, a load may be given to the ink supply port and the ink ejection port, wherein there is a fear that ink leakage occurs.
In addition, it is advantageous to increase the area, in which the annular projection is formed, as much as possible, and to increase the area of the film adhered to the tip end of the annular projection in order to increase the damper function of the passage component. However, since it is difficult to form the rib to increase the rigidity in an area surrounded by the annular projection, the rigidity may be remarkably lowered if the area in which the annular projection is formed is increased.
Therefore, where the damper function as described in JP-A-2007-268829 is given to the attachment having the ink supply passage and the ink ejection passage formed therein, there is a fear that the attachment is deformed by a force received when the attachment is mounted in an ink jet head, and ink may leak at a connection portion with the ink jet head.